零基础入门学习Python（19）：对象（4）组合、绑定

桃扇骨 2022-08-18 14:29 141阅读 0赞

# 零基础入门学习Python（19）：对象（4）组合、绑定 #

这节先介绍一下组合：即直接把需要的类放进另一种类中去实例化

>>> class Teacher:
            def __init__(self,x):
                self.teacher = x
    
    >>> class Student:
            def __init__(self,y):
                self.student = y
    
    >>> class School:
            def __init__(self,x,y):
                self.teacherSchool = Teacher(x)     #直接把需要的类放进去实例化
                self.studentSchool = Student(y)
            def printSchool(self):
                print("The school has ",self.teacherSchool.teacher," teachers and ",self.studentSchool.student," students.")
    
    >>> school = School(10,100)
    >>> school.printSchool()
    The school has  10  teachers and  100  students.

再介绍一下类、类对象和实例对象

>>> class A:       #类
            count = 0
    
    >>> a = A()        #类对象
    >>> b = A()
    >>> a.count        #类对象访问属性值即为类中属性的值
    0
    >>> b.count
    0
    >>> a.count += 10  #修改a对象属性值
    >>> a.count
    10
    >>> b.count
    0
    >>> A.count
    0
    >>> A.count += 100
    >>> b.count
    100
    >>> a.count        #a实例覆盖了类A中的count值
    10
    >>> class B:
            def num(self):
                print("num")
    
    >>> a = B()
    >>> a.num()
    num
    >>> a.num = 1      #实例化后的a创建了一个x属性
    >>> a.num
    1
    >>> a.num()        #如果属性名跟方法名相同，属性会覆盖方法，此时相当于调用不存在的方法，所以会出错
    Traceback (most recent call last):
      File "<pyshell#47>", line 1, in <module>
        a.num()
    TypeError: 'int' object is not callable

最后再介绍一下绑定：Python严格要求方法需要有实例才能被调用，这种限制其实就是Python所谓的绑定概念。

>>> class C:
            def setXY(self,x,y):
                self.x = x
                self.y = y
            def printXY(self):
                print("x = ", self.x,"y = ", self.y)
    
    >>> c = C()
    >>> c.setXY(2,7)   
    >>> c.printXY()
    x =  2 y =  7
    >>> c.__dict__     #查看对象所拥有的属性，返回字典类型
    {
       'y': 7, 'x': 2}
    >>> C.__dict__     #属性值2和7仅属于对象c
    dict_proxy({
       '__module__': '__main__', 'printXY': <function printXY at 0x02699AE0>, 'setXY': <function setXY at 0x02148738>, '__dict__': <attribute '__dict__' of 'C' objects>, '__weakref__': <attribute '__weakref__' of 'C' objects>, '__doc__': None})
    >>> del C          #删除类之后，类的对象c的属性仍然存在
    >>> c.x
    2
    >>> c.y
    7

[零基础入门学习Python（18）：对象（3）继承][Python_18_3]

[Python_18_3]: http://blog.csdn.net/qq_33256568/article/details/50388501